[Problem] To provide a porous membrane that has improved fatigue durability while maintaining permeability. [Solution] A porous membrane comprising a hydrophobic polymer as a main component, wherein the average backbone thickness of a third layer (c) is greater than the average backbone thickness of a second layer (b), and a contiguous 10 μm layer element having an average backbone thickness less than the average backbone thickness of a first layer element, where the first layer element is a 10 μm thick layer contiguous with a surface (A) in a first layer (a), is present in the first layer (a) except for the first layer element, in the second layer (b), and in the third layer (c), where the surface (A) and a surface (C) are the two surfaces of the porous membrane, and the porous membrane is divided into 3 equal parts in the thickness direction in which the first layer (a) is the layer containing the surface (A), the second layer (b) is the layer in the center portion in the thickness direction, and the third layer (c) is the layer containing the surface (C).